This invention relates to a power supply connector assembly for the heater of a pressurized water nuclear reactor pressurizer.
In a typical pressurized water nuclear reactor, a nuclear core of fissionable material is cooled by primary coolant which during operation flows past the core and picks up heat therefrom. This reactor coolant is under a considerable pressure during operation such that the heated water remains in a subcooled state.
This pressure is maintained within certain limits by means of a pressurizer, essentially an external upright pressure vessel equipped with a spray nozzle and electric heaters.
The pressurizer contains water and steam. To increase primary coolant pressure, for example during heat losses, reactor startup, and load changes causing a pressure drop, the electric heaters heat the water within the pressurizer, thereby creating more steam and displacing water to a surge line connected to the primary coolant system.
The electric heaters used to increase steam pressure are typically found within the lower section of the pressurizer. These heaters are of the direct-immersion type, sheathed in stainless steel or Inconel, and shop assembled in bundles. Each of the two or three bundles is field installed through penetrations in the vessel wall, and sealed by means of a gasketed closure. An electrical connection is then made to the end of each heater using a special fitting which provides insulation from the steam and water.
The use of special connectors or cable assemblies to provide electrical power to the pressurizer heaters in a nuclear steam generating electrical supply system is well known in the art. However, in the past, these connectors with attached power supply cabling have not been designed as an integral unit capable of operating during and after a severe environmental transient, for example a loss-of-coolant accident (LOCA) or a main steam-line break (MSLB).
Instead, these connectors have commonly been comprised of simply a standard, pin-socket type connector tied to a braided cable. As a result, there have been several incidents where pressurizer heaters were rendered temporarily inoperative due to severe adverse environmental effects. These unanticipated periods of inoperability are extremely undesirable as they may hamper control and operation of the pressurizer, and thereby the primary coolant system.
It is therefore desirable, as a solution to this recurrent problem, to design an integrated pressurizer heater power supply connector which would have the ability to resist extreme environmental conditions.